It is well-known that for burning a liquid hydrocarbon type fuel, the combustion is much more efficient and complete when the fuel is vaporized prior to being mixed with the oxygen-containing gas for combustion. The vaporization of the fuel makes possible more complete contact of the molecules of the fuel with the oxygen-containing gas than if the liquid is simply atomized into droplets of liquid, thereby ensuring complete combustion of the fuel under appropriate combustion conditions.
The prior art devices for mixing a liquid hydrocarbon type fuel with an oxygen-containing gas, such as air, conventionally atomize the fuel into droplets of liquid instead of vaporizing it. This is done in a variety of ways, the purpose being to subdivide the liquid fuel into small particles, thereby providing a maximum of surface contact between the particles of liquid and the oxygen-containing gas. Vaporization under these conditions will take place only after combustion begins, and the heat of combustion vaporizes some of the particles.
As a result of the use of the atomizing technique, if conditions for combustion are not perfectly controlled, there often results incomplete combustion of the hydrocarbon, thus increasing the carbon monoxide and hydrocarbon gas levels in the products of combustion.
In atomization devices for conventional internal combustion type engines, the fuel is normally sucked into the throat of a carburetor through a feed tube, with the air being sucked into the carburetor flowing past the end of the feed tube and atomizing the liquid flowing from the feed tube. A similar type of action takes place in a so-called injection type system, in which the liquid fuel is positively injected into the flowing stream of air. In addition to the usual problems with atomization, such system very often result in some of the fuel particles being heavier than others, and the heavier fuel particles have a tendency to separate within the airstream and cause a change in the air/fuel mixture. This adds to the production of unburned hydrocarbons in products of combustion. Not only does it add to the polluting effect of the exhaust gases and waste of fuel, but it causes engine knocking and dieseling after the ignition is turned off. This is because the heat of the engine causes the heavy fuel particles, particularly those in low octane gasoline which is now in more common use, to ignite. It is also a cause of the oily smell of Diesel engines.
Similar problems exist with oil burners, which generally atomize the liquid hydrocarbon fuel by the use of pressure on either the fuel itself being forced out of the nozzle, on the air supplied to the nozzle with the fuel, or both. Again, the effect of this action is to atomize the fuel into very small particles of various sizes, with the same atomization and combustion problems as occur in the internal combustion engines.
A few proposals have been made to heat the fuel supplied to the engines or oil burners, but at most, this heating has been to adjust the vaporization temperature and is usually to assist starting in cold weather.